I only know of one printed book on Gentoo, and that is in German and was published in 2008 and so is way out of date.
The on-line book Linux Sea uses Gentoo to teach users about Linux, so that might be of interest. Of course the on-line Gentoo Handbook is a must, and does teach you how to intall Gentoo from scratch, with explanations. If you were to print it out, it would be over 70 A4 pages.
As far as the SL binary package manager Entropy is concerned, these forums and the SL Wiki will have to be your principal resource, as there is nothing more extensive.
EDIT: This post was in reply to a post by a user who subsequently requested that his account be deleted. His post was requesting recommendations for books to help him learn more about Gentoo and SL. I have left my post here as it might be of help to someone else searching in future.

